The object of the invention is therefore to alleviate the aforesaid disadvantages.
Thus, according to the invention, there is proposed a method for diagnosing the operating condition of an exhaust-gas recirculation valve of an internal combustion engine, comprising acquisition of a measured value of a reference position of the recirculation valve at a predetermined moment corresponding to a normally closed position of the valve, calculation of the difference between the acquired reference value and a reference value acquired during a previously completed diagnostic cycle, and comparison of the calculated difference with a threshold value for detection of opening of the valve.
In this way, with each acquisition of the closed position of the valve, it is verified that the said valve is effectively closed.
According to one embodiment of this method, there is additionally calculated, following the step of acquisition of the reference value, the difference between the reference value acquired during a current diagnostic cycle and a reference value corresponding to a new recirculation valve of the same type, and the calculated difference is compared with a threshold value for detection of a malfunction of the valve.
Preferably, the reference value corresponding to a new recirculation valve of the same type is acquired during the first start of the engine.
Preferably, the values of the detection threshold for opening and malfunction each include a first term that is variable as a function of temperature and a second term corresponding to a detection threshold that is independent of temperature.
According to another characteristic of this method, the said threshold values are variable as a function of operating parameters of the engine.
The reference value acquired during the diagnostic cycle in progress is additionally stored in memory in view of a subsequent diagnostic cycle, if correct closing of the valve and the absence of malfunctions were detected during that diagnostic cycle.
According to the invention, there is also proposed a device for diagnosing the operating condition of an exhaust-gas recirculation valve of an internal combustion engine, for use of a method such as described hereinabove.
This device is provided with means for measuring the valve position, the said means being connected to a central processing unit in order to deliver thereto a measured value of the reference position of the valve, the central unit being provided with means for calculating the difference between the reference value and a reference value acquired during a previously completed diagnostic cycle, and with means for comparing the calculated difference with a threshold value for detection of opening of the valve.
According to another characteristic of this device, the central unit is provided with means for calculating the difference between the reference value and a reference value corresponding to a new recirculation valve of the same type and with means for comparing the calculated difference with a threshold value for detection of a malfunction of the valve.
For example, the means for measuring the valve position contain a measuring potentiometer.